Hip Fracture Epidemiology
According to prior art document U.S. Pat. No. 5,599,290 fractures of the proximal femur are a major source of mortality and morbidity among the elderly. Approximately 250,000 hip fractures occur in the United States annually. Nearly 33 percent of women and more than 17 percent of men will experience a hip fracture if they live to age 90. Among patients who are functionally independent prior to a hip fracture, 15 to 25 percent remain in long-term care settings for more than a year afterward. Another 25 to 35 percent are dependent on others for their mobility. More than half of those that survive hip fracture never recover normal function. Moreover, the average mortality associated with hip fracture in elderly patients is approximately 20 percent in the first year.
The public health impact of hip fractures is also staggering. Surveys in the United Kingdom have shown that at any one time about 50 percent of acute orthopaedic beds are occupied by hip fracture patients. In the U.S., the average length of hospital stay for hip fracture patient is three weeks, longer than for any other diagnosis. The annual costs associated with the acute and chronic care of hip fracture patients in the United States is estimated to exceed $7 billion. The problem can only be expected to worsen with projected increases in the average age of the world population, leading some to suggest the possibility of a nearly three-fold rise in the total number of hip fractures by the middle of the next century.
Over 90 percent of all hip fractures are caused by falls. However, the majority of falls in the elderly result in only minor injury, with one to three percent causing hip fracture. Surveys among elderly fallers have shown the following factors increase the risk for suffering a hip fracture in a fall (in order of importance): 1) impacting on the hip or side of the leg (which increases the risk of fracture by over 20-fold), 2) having a tall, slender body habitus, 3) falling with a high initial potential energy (which depends on both body mass and the height of the fall), and finally 4) possessing low bone density in the proximal femur. These results suggest the risk for hip fracture in a fall is dominated by the severity of the fall as opposed to the density and strength of the proximal femur. To reduce the incidence of hip fractures, hip fracture prevention strategies must therefore either reduce the incidence of falls, or protect the femur in the event of a fall. The former strategy may be accomplished by restricting mobility, although this carries associated medical risks and impairs personal autonomy and quality of life. It might also be accomplished through exercise programs in the elderly populations at greatest risk for falling, although no study to date has proven the effectiveness of such an approach. In any case, it seems unrealistic to expect the complete elimination of falls among the elderly, given the often multiple factors (cardiac, neural, musculoskeletal) and random causes of falls. It therefore appears that the most reliable method for reducing hip fracture incidence is to protect the femur during the impact stage of the fall. This essentially requires lowering the impact force applied to the femur to a value below its fracture threshold.
Hip fracture refers to fracture of the proximal end of the femur, which is the strongest, heaviest, and longest bone in the body, accounting for approximately one-fourth of total body height. The proximal end of the femur consists of a head, neck, and greater and lesser trochanters. The neck of the femur connects the spherical head to the shaft. It is limited laterally by the greater trochanter, a large, somewhat rectangular lateral projection from the neck and shaft, which provides an insertion site for several muscles of the gluteus region. The greater trochanter lies laterally, just beneath a relatively thin layer of skin and adipose tissue (fat), and can be easily palpated on the lateral side of the thigh. Since it is the most lateral point of the hip region, the greater trochanter is the site which comes into contact with a hard surface when one lies on one's side, and the site where the majority of impact force is applied when one falls sideways onto the hip. Consequently, falls to the side resulting in impact to the greater trochanter carry a high risk for hip fracture.
In contrast to the minimal amount of soft tissue covering the greater trochanter, a considerable quantity of soft tissue exists in the posterior gluteal (buttock) and anterior thigh regions adjacent to the greater trochanter. Upon impact to these regions, this soft tissue is able to absorb significant energy, and lower the impact forces applied to the underlying skeletal structures. Gluteal soft tissues include the gluteus maximus, medius, and minimus muscles, as well as the considerable layer of fat overlying the buttock. The most significant anterior thigh soft tissues are the quadriceps muscles, which include the three vastus muscles and the rectus femoris muscle.
Experimentally, when the elderly cadaveric femur is loaded in a configuration simulating a fall on the hip, the average force required to fracture it is 2040N [Lotz J C and Hayes W C, J Bone Joint Surg [Am], 72-A:689-700, 1990]. The corresponding average energy absorbed by the bone up to fracture is 25 J. At standing height, the potential energy of the body can be well over 20 times this amount. Previous research suggests the force applied to the femur at impact from an average sideways fall to the hip is about 6 kN, over three times the mean fracture force (Robinovitch, S N, Hayes, W C, McMahon, T A, J Biomech Eng, 113: 366-374, 1991). It therefore appears that to avoid hip fracture during a fall, one or more of the following must occur: 1) direct impact to the lateral aspect of the hip must be avoided, 2) the impact site must extend outside the hip region, or 3) significant energy must be absorbed by alternative mechanisms such as contraction of the thigh muscles during descent, breaking the fall with an outstretched hand, or deformation of both the floor and the soft tissue overlying the impact sight.
Similar to hip fracture, fracture of other bones such as the tibia, radius, and ulna occurs when the force applied to the bone exceeds that required to initiate fracture. Often such a situation arises when the impact energy is high, and contact occurs to a small area directly overlying the fracturing bony structure. In such circumstances, the impact energy cannot be absorbed and/or dissipated through a large area, and high local stresses are applied to the underlying bone.
Prior Art Protective Devices
Several protective garments have been developed with the aim of preventing hip fractures. All of these devices attempt to reduce fracture incidence by reducing the impact force applied to the femur during a fall on the hip.
A device is proposed in U.S. Pat. No. 5,599,290 and in U.S. Pat. No. 5,545,128. This solution is based on the use of shear-thickening material which is disposed in at least one protective device which is shaped in accordance with the anatomical features of the vulnerable region and the soft tissue region. This device utilizes the shear thickening behaviour of the material and its inherent ability to stiffen with a sudden impact to shunt a substantial portion of the impact energy from the vulnerable region to the soft tissue region where such energy may be safety dissipated. Moreover, the prior art documents disclose mounting means for removable mounting the protective device on the subject in such away as to permit the shunting of impact energy from the vulnerable region to the soft tissue region.
Even though the prior art technology provides a solution overcoming the above problems there would be problems associated with such protective devices. This problem is primarily due to the use of shear-thickening material which makes the device heavy and which requires the shear-thickening material to be encased in encapsulations that are able to maintain a stable form in order for the force shunting properties to be consistent and durable in wear and washing. Moreover there is a risk of shear-thickening material leaking from the encapsulations, i.e. in or after washing, due to its fluid properties.
Prior art technology also discloses garments comprising protective devices or shells based on a shunting principle, consisting of or incorporating rigid materials, i.e. in a curved or dome shaped form. However, such rigid devices have been seen to affect wearer acceptability in a negative way and a soft protective device is more comfortable to the wearer than a hard inflexible device, i.e. when sleeping on the side.
Furthermore, soft cushion or pad type products also exists, i.e. consisting of 8-18 mm thick polymeric foam material cut to i.e. a circular or oval shape, simply overlying the entire hip region. Such energy absorbing and/or dissipating materials or structures placed directly over the greater trochanter and surrounding area (Ferber, U.S. Pat. No. 4,807,301; Galton, U.S. Pat. No. 4,737,994; Kolb, U.S. Pat. No. 4,761,834; Kolsky, U.S. Pat. No. 5,034,998; Wortberg, U.S. Pat. No. 4,573,216) have the major drawback that they cover the greater trochanter and proximal femoral diaphysis, and thus transmit considerably load to these regions during impact to the hip. As described previously, these regions of the femur, and in particular the greater trochanter, extend furthest laterally of all bony components of the hip region, and are protected by a minimum of overlying soft tissue. They thus represent the regions of lowest compliance within the total protected area, and subsequently, during impact to the protective garment, the majority of impact force is transmitted to the femur.
U.S. Pat. No. 6,195,809 discloses a generally elliptical first base portion with a raised portion superimposed thereon. The raised portion is provided in the form of an open annulus having an inverted U-form. Such a product is an improvement compared to generic foam pads in a plate format as far as force attenuation goes. However, still the greater trochanter is impacted through forces directed through the base portion material.
Such prior art soft pad devices tend to cover a large area of the hip region, including the greater trochanter region, be non-breathable and thus warm to wear, and therefore attempts have been made to increase breathability and reduce heat i.e. by providing a plurality of smaller holes on the device surface area. Other commercially available soft pad devices have a small circular hole in the pad centre (diameter approx. 2-2.5 cm), according to the manufacturers instructions to enable that the wearer or caregiver can check with a finger if the device is positioned correctly, centred around the greater trochanter.
As previously mentioned, such soft pad devices are by large energy absorbing and have the drawback that they still transmit a substantial portion of the energy directly to the greater trochanter, as they directly overlie the greater trochanter. Thus, they have to be relatively thick in order to be somewhat efficient, which makes them bulky when worn and warm to wear which again leads to lower wearer acceptability.
It is the object of the present invention to provide a solution to the above problems by providing a garment, a device and a method for reducing the risk of bone fracture which would comprise a lightweight soft and protective device which is comfortable and less warm for the wearer and which maintain a stable form and which makes it possible to shunt, absorb and retransmit a substantial part of the impact energy to the soft tissue region surrounding a vulnerable region.